Barney the New Caledonian crow appears to be a wilier bird than even the scientists used to his resourcefulness may have realised. Already adept at using sticks to forage for food, he has now been observed using them to inspect foreign objects that could potentially be threatening.

How bright does that make him in the grand pecking order of animals? There are no measures for assessing avian IQ, but the New Caledonian crow appears to be in a league of its own in performing tricks with sticks, something celebrated in a Guardian In Praise of leading article last year.

This followed tests in which scientists from New Zealand and Oxford set captive crows a three-stage problem. They had to get a short stick by pulling up a string, use that stick to winkle out a long stick from a toolbox, and then use the long stick to extract food from a hole. They managed it successfully.

"Evidence is building up that they're able to plan their actions in advance, which is very interesting from a cognition point of view," says research zoologist Dr Joanna Wimpenny, a member of the Oxford team. "It isn't just that they're responding in a pre-programmed sort of way. It seems possible they may potentially view a problem and know what the answer is."

If prolonged existence is all about the survival of the fittest, New Caledonian crows, whose home is a remote island in the South Pacific, seem set to thrive. Masters at using sticks to find nutritious beetle grubs from trees in their forest habitat, zoologists are now assessing the evolutionary implications of their diet. Does, for instance, their lifestyle result in fitter and healthier offspring?

The more these intriguing birds are observed by scientists, the more an apparent intelligence comes to light. Further experiments carried out at Oxford suggest they can also use sticks as tools to inspect all sorts of objects, possibly to assess whether or not these present a danger. It's the first time birds have ever been observed using a tool for more than one purpose.

Five pairs of crows underwent tests at the university's aviaries to see how they would react to a variety of objects, carefully chosen so the birds wouldn't be tempted to view them as a possible source of food. As a further precaution, all the crows had been fed beforehand.

The researchers had an inkling their test might reveal something new. "We decided to do the experiment because they'd been seen using tools to pick at random objects such as a spider motif on a piece of cloth," said Wimpenny.

Their hunch proved right: the studies revealed that on eight occasions, a bird's first contact was by using a tool. In all three trials, Barney began by using a stick for inspection. One involved a rubber snake, which he first approached, but did not touch, before retreating to pick up a stick. He twice stopped short of touching the snake before using the tool to prod it. After this, he dropped the stick and tugged at the tail, instantly jumping back. Then, having prodded the snake again, he discarded the stick and carried on pecking at it "in a noticeably less hesitant manner".

In other experiments, two different birds, Pierre and Corbeau, also made a first approach with tools on three separate occasions. Pierre used a short piece of woodchip to touch a flashing light within two seconds of picking it up; while Corbeau was seen prodding a metal toad after 10 seconds; and a rubber spider after 35 seconds.

Most tool-using species only use their aid of choice for a single specific reason. "Birds have never before been observed using a tool for more than one purpose," said Wimpenny. "It was really exciting."

Scientists concluded that the crows' "jumpy behaviour" before and during their first interaction with some objects was very different to their demeanour when extracting food. Moreover, they tended to use the sticks only to make first contact. Subsequently, they either ignored the object or dropped the tool to peck at it – not something they do when searching for food.

The behaviour of Barney et al raises many questions. "There are many different ways this research could go," Wimpenny said. "For instance, at the moment we have no idea about their social learning abilities – we don't know if they'll learn from other individuals, though we are getting a few clues."

Does this make them, intellectually speaking, alpha birds? Scientists are reluctant to categorise them thus. "Asking how intelligent they are is really tricky – other birds excel at other things such as developing social cognition," she said.

Scientists want to find out much more about how the crows behave in their native habitat. But amid New Caledonia's mountainous forest, they prove elusive. Wimpenny's fellow researcher Dr Christian Rutz, soon to return from three months on the island, has, in the past, sought to overcome the problem by attaching tiny cameras to the base of their tails.

Rutz is part of a team involving Oxford and Exeter universities continuing to investigate the crows' foraging lifestyle, specifically to see if it gives them any possible "evolutionary advantage". He believes it probably does – the grubs they harvest are so energy-rich and full of fat that just a few specimens can satisfy their daily needs.

With crows so hard to pin down in the wild, scientists have devised an alternative approach to try to analyse what's happening. The grubs they feed on have a distinct chemical fingerprint – stable isotope profile – traceable through feathers and blood. Thus researchers can collect samples to work on "with little or no harm to the birds".

"By comparing profiles of the crows' tissues with those of their … food sources, we can estimate the proportion of larvae in crow diet," says Rutz. This should enable scientists to gauge the extent to which individual birds depend on using sticks to feed themselves.

Sample analysis has been conducted at Exeter University that has helped to develop statistical models that enable tissue-profile comparisons to be carried out. "The approach we used is very similar to that employed by forensic scientists trying to solve crimes and has even appeared on CSI," says Dr Stuart Bearhop, associate professor in conservation biology. The team believes this research could be a suitable model for studying what happens to other animal tool-users such as chimpanzees.

Much work has yet to be done before any conclusions can be drawn. "The real difficulty and interest in understanding a particular animal's intelligence is putting it into the context of the ecological circumstances in which it is found," says Professor Alex Kacelnik, professor of behavioural ecology at Oxford and a co-author of the report on how New Caledonian crows use tools when not looking for food. "We're trying to understand the physical processes by which an animal uses objects, and what role its behaviour plays in the wild."